The proposed research will test the hypothesis that a pattern of mechanical ventilation utilizing high frequency (5-15 Hertz), low volume (2-5 ml/kg) oscillations (HFO) will be effective and safe in the treatment of neonatal pulmonary disorders. Studies will be conducted in the first hours after birth using an experimental model of hyaline membrane disease (HMD), the prematurely delivered Macaca nemestrina. Use of this animal model will allow a detailed examination of both clinical effects and of modifications of surfactant metabolism and parenchymal histology, when compared to animals with HMD treated by conventional mechanical ventilation. Additional studies with one day old lambs ventilated with HFO will be conducted using the multiple inert gas elimination technique to delineate patterns of ventilation-perfusion matching. These latter studies will utilize inspired gas mixtures of differing mixed venous blood to mixed expired gas. Results should contribute to understanding the processes of intrapulmonary gas transport occurring with HFO. The proposed work will allow the careful evaluation of a potentially important new tool in neonatal care. The results should make any application of HFO to newborns both safer and more effective.